Function updateElement

packages/react-reconciler/src/ReactChildFiber.js:559–615

(
    returnFiber: Fiber,
    current: Fiber | null,
    element: ReactElement,
    lanes: Lanes,
  )

  }

  function updateElement(
    returnFiber: Fiber,
    current: Fiber | null,
    element: ReactElement,
    lanes: Lanes,
  ): Fiber {
    const elementType = element.type;
    if (elementType === REACT_FRAGMENT_TYPE) {
      const updated = updateFragment(
        returnFiber,
        current,
        element.props.children,
        lanes,
        element.key,
      );
      if (enableFragmentRefs) {
        coerceRef(updated, element);
      }
      validateFragmentProps(element, updated, returnFiber);
      return updated;
    }
    if (current !== null) {
      if (
        current.elementType === elementType ||
        // Keep this check inline so it only runs on the false path:
        (__DEV__
          ? isCompatibleFamilyForHotReloading(current, element)
          : false) ||
        // Lazy types should reconcile their resolved type.
        // We need to do this after the Hot Reloading check above,
        // because hot reloading has different semantics than prod because
        // it doesn't resuspend. So we can't let the call below suspend.
        (typeof elementType === 'object' &&
          elementType !== null &&
          elementType.$$typeof === REACT_LAZY_TYPE &&
          resolveLazy(elementType) === current.type)
      ) {
        // Move based on index
        const existing = useFiber(current, element.props);
        coerceRef(existing, element);
        existing.return = returnFiber;
        if (__DEV__) {
          existing._debugOwner = element._owner;
          existing._debugInfo = currentDebugInfo;
        }
        return existing;
      }
    }
    // Insert
    const created = createFiberFromElement(element, returnFiber.mode, lanes);
    coerceRef(created, element);
    created.return = returnFiber;
    if (__DEV__) {
      created._debugInfo = currentDebugInfo;
    }
    return created;
  }